Access Tab - Not saving editor rights

I'm trying to apply edit rights to specific pages for specific groups (The client would like sections to edit their own pages but only their own pages). I've created the appropriate groups - one per section - and added the logins for the administrators of each section. I've also set the access rights (For testing I've just added "Access to all CMS Interfaces").

I'm going through the site and trying to set edit rights. I choose "Only these people" and select "Administrators" and my sub-section group and then Save. If I then refresh the window in the CMS (or navigate to a different page then back) the radio button for "Only these people" is still selected byt the pull down is blank again. Also if I log in as a user from the sub-section the pages are all greyed out (including the page I should be able to edit).

I've attached screenshots of the Security settings for the group and the access tab of one of the affected pages. This fault affects all pages in the site.